Refrigeration



March 14, 1944- y s. P. soLlNG ETAL 2,344,215

REFRIGERATION Filed Feb. 26, 194s 2 sheets-sheet 1 .THEEMosTAT/c F1 G. 2

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PRESSURE M/TCH ttornegs Patented Mar. 14, 1944 UNITED REFRIGERATION Samuel l. Soling and Henry B. Pownall, York, Pa., assignors to York Corporation, a corporation oi.' Delaware Application February 26, 1943, Serial No. 477,244

13 Claims. (Cl. 62-6) This invention relates to refrigerative circuits of the compressor, condensed evaporator circuit type, and probably has its principal field of use in cases where the plant is used to maintain low temperatures, and where the resulting temperature is automatically controlled by regulating the operation of the refrigerating unit.

Control of temperature by starting and stopping the compressor is objectionable where frequent starts and stops are necessary or likely to occur. Control of suction pressure by a suction pressure regulator is undesirable where conditions are such as to lead to very low suction pressure beyond the suction pressure regulator, as this may lead to loss of oil for the compressor crank case, or serious heatingof the compressor,

Where conditions are such as to render both these prior methods undesirable, the present inventionV proposes to keep the compressor continu-l ously in operation, and when temperature is unduly low to supply an artificial heat load to the evaporator by bleeding thereto a limited amount of hot gas from the compressor. From the standpoint of eiiiciency this is not economical, but in many cases freedom from mechanical diillculties attendant upon the use of the prior practices (which also involve as a practical matter some loss of overall efficiency), justifies the procedure. Where sustained operation yunder diiiicult conditions is a prime requisite the proposed control has outstanding advantages, because it gives control without endangering the compressor.

Six embodiments of the concept as arranged for use in cooling air are illustrated in the accompanying drawings, in which- Fig. 1 is a diagram showing a system of the on and oi type in which the artificial load is controlled directly by temperature.

Fig. 2 shows a modication of the structure of Fig. 1 designed to give progressive control.

' ing 26.

by the lclosing and opening of switch 21 which l Fig. 3 is a view similar to Fig. 1 showing the articial load controlled by suction pressure.

Fig. 4 shows a modiiication of the structure of Fig. 3 designed to give progresive control.

Fig. 5 is a similar view. showing how the invention may be applied toa cascade system, i. e., one in which the condenser of the low temperature circuit is cooled-by a second refrigerating circuit. l

Fig. 6 shows .the invention applied to a compound circuit with intermediate liquid cooler.

Refer to Fig. 1. The compressor is shown at II,`the condenser at I2 andthe evaporator at I8. The evaporator is shown as mounted in an air duct I4 through which air to be cooled is propelled in the direction of the arrow.

Refrigerant compressed in the. compressor flows through the hot gas line I5 to the vcondenser. Liquid from the condenser ilows through the liquid line i6 to the thermostatic expansion valve il which delivers to the evaporatorthrough a line IB Whose length is exaggerated in the diaphragm. From the evaporator the suction line I9 leads to the compressor.

The thermostatic expansion valve il is of the well known type in which a thermostaticv bulb 2l applied to suction line I9 near the evaporator exercises a supervisory control to assurev that refrigerant leaving the evaporator is in the vapor phase and slightly superheated. The usual connecting capillary appears at 22.

The circuit so far described is conventional.

To control the circuit in response to the temperature of the air leaving the evaporator, use is made of a by-pass line 23 which leads from the hot gas line to a point in the low side between expansion valve I1 and thermostatic bulb 2i and advisably between valve il and evaporator I3. This by-pass is controlled by valve means responsive to the indications of a thermostat bulb 24 subject to the temperature of the cooled air.

'Ihe valve controlshown in Fig. 1 isof the on-and-off or positive type. The control is exercised by valve 25 which is actuated by wind- The latter is energized or deenergized is shifted by bulb 24. The valve 28 is simply an adjustable throttle to limit the rate of ow through .the by-pass. It protects valve 25 from erosion, since there needbe no throttling at valve 25 when the latter is open.

Substitution. of a gradual acting valve forv valve 25 and a gradual controller for switch 21 renders valve 28 unnecessary, since gradual action entails throttling in the gradual acting valve itself.

Such an installation is indicated in Fig. 2, in which corresponding parts are similarly numbered' with the distinguishing letter a. Here a gradual acting pneumatic thermostat is dagrammed. The bulb 24a actuates a controller 21a whose branch` line leads to diaphragm motor 26a connected to actuate valve 25a.

Both types of thermostatically actuated valve are known, and the control eected is the samew except asto gradual or on-and-oii.' characteristics. [in either case, fall of` temperature at the thermostatic bulb has the effect of opening the by-pass, either gradually, or suddenly when I suction pressures, the control may be exercised by suction pressure.

Fig. 3 shows such a scheme applied to the same circuit as is shown in Fig. 1. identical with those in Fig. 1 have the same reference numeral with the letter b. 'I'he difference is the substitution for thermostat bulb 24 and switch 21 of a pressure switch 29 which responds to pressure in suction line |9b and controls Winding 26h so that valve .25h opens if suction pressure falls too Tow, thus supplying an articial heat load to the evaporator.

Since the by-pass delivers to the suction line, the valve h is in effect a pressure reducing valve responsive to pressure on its discharge side. Various pressure reducing valves of this class could be substituted Ain the arrangement shown in Fig. 3. n An example of this is shown in Fig. 4. The parts 29, 25h, 2Gb and 28h of Fig. 3 are wholly omitted and a pressure reducing valve 3| is interposed near the junction of the by-pass 23o and the pipe |8c. In Fig. 3, for circuit components, the numbering used on Figs. 1 and 2 is adopted but with the letter c. The valve 3| is of the type which responds to its own discharge pressure and 32 indicates its pressure control connection.

In any case the by-pass should deliver hot ga to the low pressure side at a point between the Vvalve |1 (or its analog) and bulb 2| (or its analog) so that heat to control valve |1 always shall be available. The distinction between this arrangement and prior art proposals to bleed gas directly from the compressor discharge to the compressor intake should be appreciated. The present invention supplies a heat load to the evaporator and avoids all risk of overheating the compressora fault inherently present in all short circuiting schemes.

Because the invention is particularly useful with low temperature systems and can be applied to cascade systems commonly required in low temperature work. it is illustrated as so embodied in Fig. 5. It is there applied to the low temperature circuit.

The circuit which cools the condenser of the low temperature circuit comprises a compressor 4|, hot gas line 42, condenser 43, and liquid line 44 rwhichleads through the superheater 45 to expansion valve 46.

The superheater 45 is simply a shell and tube exchanger in which the warm liquid from condenser 43 flows around the tubes to deliver heat to the cold suction gases of the low temperature circuit which ilow through the tubes.

Expansion valve 46 delivers to exchanger 41. This is a shell and tube exchanger which serves as evaporator for the circuit being traced and condenser for the low temperature circuit. Refrigerant expanded through valve 46 flows through the tubes to suction line 48 and so back to compressor 4|'. Valve 48 is of the superheat controlled type and has the usual thermal bulb 50 and connecting capillary tube 49.

'Ihe low temperature circuit comprises a com- Components 'I'his discharges through connection -55 to evaporator 56. 'I'he suction line 51 leads thence .through superheater 45 to the compressor 5|.

The expansion valve 54 is of the superheat controlled type and its thermal bulb 58 is located v scribed for Fig. l.

on the suction line 51 beyond exchanger (superheater) 45 and is connected by capillary tube 56.

The exchanger 45 is called a superheater because its function is to -warm refrigerant leaving evaporator 56, and assure that it is superheated'. Ordinarily the heat available at evaporator 56 is not sufllcient to assure this.

The by-pass. characteristic of the invention, is the pipe 6| which leads from hot gas line 52 to a point in the low side beyond expansion valve 54 and in advance of bulb 58. It is controlled by valve 62 which is actuated by winding 63. A thermostatic :bulb 64, subject to the temperature of the cooled air controls switch 65 and this in turn controls winding 63. A throttle valve 66 is yused for the same purpose as is valve 28 of Fig. 1.

The by-pass control is the same as that decan be substituted. Similarly, controls responsive to suction pressure (in line 51) can be used in the ways suggested in Figs. 3 and 4.

Another system extensively used for low temperature refrigeration involves the use of two compression stages with an intermediate liquid cooler of the direct expansion type. 'I'he invention is shown applied to a system of this description in Fig. 6.

In this figure the low stage compressor is indicated at 1| the compressor discharging through vinterstage connection 12 to the intake of the high stage compressor indicated at 13. From compressor 13 the hot gas line 14 leads to the condenser 15 from which liquied refrigerant drains into the receiver 16. The liquid line 11 leads from the receiver through the tube 18 within the shell of the liquid cooler 19. The liquid cooled by passage through this tube is delivered to the main expansion valve 8|. Ihe valve 8| delivers through connection 82 to the evaporator 83. 'I'he evaporator 83 is the low temperature element of lle circuit and carries the main refrigerative loa From the evaporator 83 the suction line 84 leads to the intake of compressor 1| by way of the tubes 85 within the shell and tube superheater 86. Thermal bulb 81 of the expansion valve 8| senses the temperature in the suction line between the superheater 86 and the intake of compressor 1| and is connected by capillary 88 with the expansion valve 8|. A branch liquid line 89 leads from the liquid line 11 to a space within the superheater shell 86 around the tubes 85 so that warm liquid delivered through the line 88 exchanges heat with the cold vaporous refrigerant owing from the evaporator 83. The liquid so cooled ilows by line 9| to a second expansion valve 92 which expands refrigerant into the interior o1 the cooler shell 19 around the tube 18. From the shell 19 a suction line 93 leads to the interstage line 12 and consequently to the suction A progressive valve control' to the interstage line 'I2 at a point between the junction of line 93 therewith and the intake of the high stage compressor 13. Ihe thermal bulb 94 is connected by capillary 95 with a thermostatic expansion lvalve 92. It is probably unnecessary to remark that each of the expansion valves is of the superheat control type.

To give thermal control while maintaining the compressors constantly in operation, compressed non-condensed refrigerant is delivered to the evaporator 83. The preferred arrangement is to lead the branch line 96 from the discharge line 1I of =the high stage and it is so shown. However, it could be branched off with similar effect from the interstage connection 'l2 preferably between the compressor 1| and the junction of 12 with line 93. Whichever way the line 96 is connected, it delivers compressed gaseous refrigerant through valve 91 and manually adjustable controlling valve 98 to the inlet connection 82 of the evaporator 83. y

Various controls already outlined could be used but in the example illustrated, a thermal bulb 99 controls the thermostatic switch IUI which operates the valve 91 through the winding IIJ2. In other words, the type of control shown in Figs. 1 and 5 is illustrated in the embodiment of Fig. 6 with the understanding that alternative arrangements responsive, for example, to the suction pressure in line 84 might be substituted as in the simpler forms above described. Also the thermostatic control illustrated might be of the progressive type as indicated in Fig. 2, these being matters of detail within the broad scope of the invention.

It should be noted that in Fig. 6 as in Fig. 5,

e use is made of a superheater to deliver heat in the suction line from the main evaporator between the evaporator and the thermal bulb which controls thev main expansion valve. In Fig. 5 there are two distinct but inter-related refrigerant circuits. In Fig. 6 there is a main circuit and a secondary circuit which is distinct to the extent that it forms a by-pass around the evaporator portion of the main circuit. The use of the superheater in such circuits is believed to be novel and is here illustrated .because it is an important factor in satisfactory operation of systems of this type including the present invention.

The circuits including the superheater are believed to be novel in themselves but are not claimed herein because not the joint invention of the present applicants.,

Basically the invention contemplates controlled delivery of hot gas to the evaporator, beyond the expansion valve to supply an artificial heat load. This regulates the cooling effect and protects the compressor against unduly low suction pressuresand attendant evils such as heating, and loss of oil from the compressor crank case.

To indicate the Wide applicability of the principle, several embodiments have been described, but these are merely examplary.

While the scheme is inefcient Where the bypass is open for considerable periods, the comparison with existing control schemes is not unfavorable. Continued operation at abnormally low suction pressure, and short cycling are each inefficient, and areeach harmful to the mechanism. The invention without great impairment of emciency avoids harm to the mechanism and hence is greatly to be preferred in applications to which it is suited.

Whatis claimed is:

1. 'I'he combination of a refrigerative circuit of the compressor, condenser, evaporator type, including an expansion valve interposed between the condenser and the evaporator, and thermostatic means subject to the temperature of refrigerant between the evaporator and compressor and exerting a controlling influence on the expansion valve; a by-pass whose flow capacity is less than the output of the compressor for delivering compressed uncondensed refrigerant to a point in the circuit between the expansion valve and said thermostatic means; and means for controlling now through the by-pass.

2. The combination of a refrigeratlve circuit of the compressor, condenser, evaporator type. including an expansion valve interposed between the condenser and the evaporator, and thermostatic means subject to the temperature of refrigerant between the evaporator and compressor and exerting a controlling influence onthe expansion valve; a yby-pass whose flow capacity is less than the output of the compressor for delivering -compressed uncondensed refrigerant to a point in the circuit between .the expansion valve and the evaporator; and means for controlling flow through the by-pass.'

3. The combination defined in claim 1 in which the means for controlling flow through the bypass is actuated by means responsive to a temperature established by the evaporator.

4. The combinationdened in claim 1 in which the means for controlling flow through the bypass is arranged to respond to suction pressure in the circuit.

5. The combination defined in claim 1 in which the means for controlling the by-pass is a pressure reducing valve responsive to pressure existing on its discharge side.

6. A refrigerative system of the compressor, condenser, evaporator circuit type, having two evaporators, one of which operates at a relatively low suction pressure and the other at a higher suction pressure; a heat exchanger for delivering heat from liquid refrigerant flowing to the second named of said evaporators to refrigerant vapor flowing from the first named of said evaporators; and controllable means for delivering compressed uncondensed refrigerant to the first named of said evaporators.

7. A refrigerative system of the compressor,

condenser, evaporator circuit type, having two evaporators, one of which operates at a relatively low suction pressure and the other at a higher suction pressure; a heat exchanger for delivering heat from liquid refrigerant flowing to the second na-med of said evaporators to refrigerant vapor flowing from the rst named of said evaporators; an expansion valve of the superheat control type controlling the supply of liquid refrigerant to the first named evaporator, said valve having a thermal element subject to the temperature of vaporous refrigerant leaving said interchanger; and controllable means for delivering compressed vaporous refrigerant to a point in the circuit between said expansion valve and thermal element.

8. The combination of the structure defined in claim 7 and means operating in relation to temperature conditions at the flrst named evaporator connected to actuate said controllable means to deliver vaporous refrigerant when temperai ture falls abnormally low and close it at other rator circuit type, the second operating in a lower temperature range than the first. said circuits exchanging heat through two surface interchangers, one of which interchangers serves as the evaporator of the rst circuit and the condenser of the second circuit, and the second of which exchangers transfers heat from the warm liquid refrigerant of the first circuit to cold vapor leaving the evaporator of the second; and controllable means in the second circuit for delivering compressed vaporous refrigerant to the evaporator of that circuit.

l0. The combination of ltwo refrigerative circuits each of the compressor, condenser, evaporator circuit type, the second operating in la. lower temperature range than the first, said circuits exchanging heat through two surface interchangers, one of which interchangers serves as the evaporator of the first circuit and the condenser of the second circuit, and the second of which exchangers transfers heat from the warm liquid refrigerant of the first circuit to cold vapor leaving the levaporator of the second; an expansion valve in the second circuit controlling delivery of liquid refrigerant to the evaporator; thermostatic means subject to temperature of refrigerant in the second circuit beyond the second heat exchanger, and exercising a controlling effect on the expansion valve; and controllable means in the second `circuit for delivering compressed vaporous refrigerant to a point in the second circuit between the expansion valve and said thermostatic means.

11. The combination of two refrigerative circuits each of the compressor, condenser, evaporator circuit type, the second operating in a lower temperature range than the first, said circuits exchanging heat through two surface interchangers, one of which interchangers serves as the evaporator of the first circuit and the condenser oi' the second circuit, and the second of which exchangers transfers heat from the warm liquid refrigerant of the first circuit to cold vapor leaving the evaporator of the second: an expansion valve in the second circuit controlling delivery of liquid refrigerant to the evaporator; thermostatic means subject to temperature of refrigerant in the second circuit beyond the second heat exchanger, and exercising a controlling effect on the expansion valve; controllable means forming a by-pass related to the second circuit for delivering compressed vaporous refrigerant to a point in that circuit between the expansion valve and said thermostatic means; and means operating in relation to temperature conditions at the evaporator of the second circuit and connected to actuate said controllable means to open the by-pass when temperature falls abnormally low and close it at other times.

12. A refrigerative system of the compressor, condenser, evaporator circuit type having two evaporators, one of which operates at a relatively low suction pressure and the other at a higher suction pressure; and controllable means for delivering compressed uncondensed refrigerant to the first named of said evaporators.

13. The combination of two refrigerative circuits each of the compressor, condenser, evaporator circuit type, the second circuit operating in a lower temperature range than the rst, and the evaporator oi' the first circuit serving as the condenser of the second circuit; and controllable means in the second circuit for delivering compressed uncondensed refrigerant to the evaporator of that circuit.

. SAMUEL P. SOLING.

HENRY B. POWNALL. 

